DOCSIS Technology

Data over cable service interface specification (DOCSIS) is a standard for broadband cable transmission of IP data services. It defines an upstream and downstream channel to enable bidirectional communications between a cable modem termination system (CMTS) in the cable headend and a subscriber's cable modem (CM).

Various versions of the standard have been established due to regional differences in cable TV bandwidth. The original American DOCSIS standard works with a 6 MHz channel bandwidth while the European EuroDOCSIS uses 8 MHz channels.

There have been five generations of the standard with ever increasing transmission rates since it was initially adopted in 1998: DOCSIS 1.0, 1.1, 2.0, 3.0 and DOCSIS 3.1. The latest generation, DOCSIS 3.1, was released in October 2013 and offers several significant improvements over its predecessors. The most important innovations include LDPC error correction, OFDM modulation and very wide channel bandwidths of up to 192 MHz in the downstream and up to 96 MHz in the upstream. The following table provides a comparative view of key parameters.

Downstream

Downstream

Upstream

Upstream

Version

DOCSIS 3.0

DOCSIS 3.1

DOCSIS 3.0

DOCSIS 3.1

Channel bandwidth

6 MHz or 8 MHz

24 MHz to 192 MHz

0.2 MHz to 6.4 MHz

6.4 MHz to 96 MHz

Modulation

single carrier

OFDM

single carrier

OFDM

QAM order

up to 256 QAM

up to 4096 QAM

up to 64 QAM

up to 4096 QAM

Multiple access method

TDMAS-CDMA

OFDMA

FEC

Reed Solomon

LDPC/BCH

Reed Solomon

LDPC/BCH

DOCSIS 3.1 also establishes new downstream and upstream frequency ranges. The overall frequency range will be extended in two stages: first to 1218 MHz and then to 1794 MHz.

Current and future channel loading

These improvements enable DOCSIS 3.1 to achieve transmission rates of up to 10 Gbit/s in the downstream and 1 Gbit/s in the upstream.

Initial DOCSIS 3.1 field tests took place in 2015. Operators will begin switching their networks to DOCSIS 3.1 in 2016. Mixed DOCSIS 3.0 and 3.1 operation will be possible during the transition.